This invention relates to a multi-cylinder internal combustion engine and, in addition, to a method for operating a multi-cylinder internal combustion engine.
Swiss patent CH 310325 discloses a method for operating an internal combustion engine having valves which are used for the charge cycle, in which method a flow connection is established—by opening an additionally provided additional valve—between the combustion chamber of an internal combustion engine and an exhaust line which is assigned to the internal combustion engine. The additional valve is continuously opened in the braking mode of the internal combustion engine, producing a braking effect. This increases the braking work which is applied when the associated motor vehicle is braked.
The object of the invention is, in contrast with the above, to provide an internal combustion engine and a method for operating an internal combustion engine with which regeneration of an exhaust gas cleaning unit which is assigned to the internal combustion engine can be promoted effectively and efficiently when necessary. This object is achieved by an internal combustion engine and by a method as claimed.
At least one of the cylinders of the internal combustion engine according to the invention has, in addition to the usual inlet and outlet valves which are used for the charge cycle, an additional outlet valve through which, in the opened state, a flow connection is established between the combustion chamber and the exhaust line. In addition, an exhaust gas cleaning unit is arranged in the exhaust line which is assigned to the cylinders of the internal combustion engine. An exhaust gas composition and/or exhaust gas temperature which are changed compared to the normal operating mode and promote the regeneration of the exhaust gas cleaning unit can be set in conjunction with a regeneration operating mode for regenerating the exhaust gas cleaning unit by activating the additional outlet valve of at least one cylinder.
Preferably a particle filter and/or a catalytic converter such as, for example, a nitrogen oxide accumulator-type catalytic converter are provided as an exhaust gas cleaning unit. In addition, it is of course possible for further components which are used for cleaning the exhaust gas to be arranged in the exhaust line. In particular for regenerating such an exhaust gas cleaning unit it is advantageous if the latter is supplied with an exhaust gas at a raised temperature and/or with a composition which is changed compared to the normal operating mode, for example with an increased content of reducing components.
Customary measures for this comprise intake-end or exhaust-gas-end throttling, combustion-end measures such as changing the fuel injection point or feeding fuel or secondary air into the exhaust section upstream of the corresponding exhaust gas cleaning unit. These measures are usually associated with a high degree of expenditure on equipment or have other disadvantages.
Consequently, the setting of the aforesaid exhaust gas properties which bring about or promote regeneration is carried out by activating, i.e. by at least temporarily opening the additional outlet valve of at least one cylinder of the internal combustion engine. Since a connection is established between the combustion chamber and the exhaust line by the opened additional outlet valve, it becomes possible for the exhaust gas conditions to be influenced in the aforementioned way by means of the respective conditions in the combustion chamber of the cylinder, and for regeneration of an exhaust gas cleaning unit to be promoted. This applies both to over-run conditions with power drain and to a traction mode with power being output by the internal combustion engine.
In particular in internal combustion engines which from the outset already have a cylinder with an additional outlet valve, for example what is referred to as a decompression valve, in order to use the internal combustion engine as a vehicle brake, the additional expenditure on equipment and the effort involved in application are low. In addition, the worsening of the efficiency of the internal combustion engine when the additional outlet valve is activated can generally be kept small so that there is only a small additional consumption of fuel.
The internal combustion engine according to the invention may have just a single cylinder with an additional outlet valve. However, typically a plurality of cylinders, in particular all the cylinders, of the internal combustion engine have an additional valve.
In a refinement of the invention, when the additional outlet valve is activated at least one cylinder can be operated with a fuel supply which is reduced compared to the operating mode without activation of the additional outlet valve. At a specific operating point, in particular at an operating point at which there is provision for the exhaust gas cleaning unit to be regenerated, it thus becomes possible at the same time to activate the additional outlet valve at least one cylinder as well as operate with a reduced fuel supply compared to the fuel supply which is normally provided at this operating point. In order to set the fuel supply to the cylinders, an injection system which permits cylinder-selective actuation is preferably provided. Said system may be a common rail system, a system according to the pump-nozzle principle or some other system with injectors which can preferably be actuated individually. The change in the fuel supply also includes their complete shutdown. The exhaust gas temperature and/or the exhaust gas composition can be influenced particularly precisely and sensitively with this refinement of the invention.
In a further refinement of the invention, when there is at least one cylinder with an additional outlet valve the additional outlet valve can be activated in a clocked fashion such that when there are a multiplicity of working cycles the additional outlet valve is opened in each case in the region of the top dead center in the compression stroke and is otherwise closed. For this embodiment there is preferably provision for the drive of the additional outlet valve to be constructed in such a way that it is decoupled from the drive for the normal charge cycle valves of the internal combustion engine. For example a separate electromagnetic drive is advantageous for the additional valves. The additional valves are preferably to be opened approximately in the region of 90° crank angle before the top dead center to 90° after the top dead center. When an additional outlet valve opens before the top dead center, it becomes possible for unburnt fuel to pass over into the exhaust section. Opening after the top dead center mainly results in an increase in the exhaust gas temperature.
In a further refinement of the invention, a cylinder group which is formed from at least two preferably adjacent cylinders with an additional outlet valve is provided. The cylinder group is preferably selected in such a way that fluctuations in the torque or in the synchronous running are minimized when the additional outlet valves are activated. For example, in a six-cylinder series-mounted engine it is possible to provide an additional outlet valve only at the first and second cylinders. In the same way it is possible in an internal combustion engine which is embodied as a V-mounted engine to provide additional outlet valves only at the cylinders of one cylinder bank. This keeps the structural complexity correspondingly low.
In a further refinement of the invention, when there are at least two preferably adjacent cylinders with an additional outlet valve there is provision for the additional outlet valve to be activated. For example in an internal combustion engine with a plurality of cylinders with an additional outlet valve it is advantageous to activate the additional outlet valves in a chronologically alternating fashion at, in each case, two adjacent cylinders in conjunction with a regeneration operating mode. This keeps in particular the thermal loading on the respective cylinders low. If all the cylinders of a six-cylinder internal combustion engine are provided with an additional outlet valve, it is possible, for example, to activate the additional outlet valve alternately at cylinder 1 and 2, cylinder 3 and 4 and cylinder 5 and 6.
In a further refinement of the invention, at least two cylinders are provided with an additional outlet valve and the number of cylinders at which the additional outlet valve is activated can be set in a variable fashion, in particular as a function of the exhaust gas temperature. This embodiment is particularly advantageous if all the cylinders of the internal combustion engine have an additional outlet valve. Depending on the thermal demand of the exhaust gas cleaning unit, when there are two or more adjacent cylinders the additional outlet valves can preferably be activated in synchronism or in each case in phase with the position of the piston of the respective cylinder. In this way it is possible in particular to set the input of heat into the exhaust gas cleaning unit very precisely and in accordance with the demand.
In a further refinement of the invention, when there is at least one cylinder with an additional outlet valve, operation with a closed additional outlet valve and with a fuel supply which is reduced compared to the normal operating mode becomes possible. As a result, in addition to influencing the exhaust gas temperature and/or exhaust gas composition in the special operating mode of regeneration of the exhaust gas cleaning unit, it is additionally possible to influence the power output in the normal operating mode of the internal combustion engine. When the fuel supply is reduced to zero, over-run shut-off is made possible under over-run conditions. It is particularly advantageous that regeneration of the exhaust gas cleaning unit also becomes possible in this operating mode, or can be continued, since an additional outlet valve can also be provided at one or more further cylinders, and these cylinders can be operated with the additional outlet valve activated. In this way, the input of heat into the exhaust gas cleaning unit is maintained. The cylinders with an activated additional outlet valve can be operated with a reduced fuel supply here if appropriate.
In a further refinement of the invention, the regeneration operating mode can be set when the additional outlet valve of at least one cylinder is activated in an operating range with reduced power output by the internal combustion engine. In particular in an internal combustion engine which operates according to the diesel principle, the input of heat into the associated exhaust gas cleaning unit is frequently low in the lower partial load range so that said unit does not always reach its appropriate temperature or drops below it. In order to reach the desired temperature of the exhaust gas cleaning unit, there is therefore provision for one or more of the additional outlet valves to be activated below a predefinable load point in the partial load range of the internal combustion engine. Above the predefinable load point of the internal combustion engine, the additional valve remains closed in the traction mode of the internal combustion engine. This additionally ensures that the additional valve or components which conduct exhaust gas are not overheated. In order to regulate the input of heat into the exhaust gas cleaning unit in the partial load range it is additionally possible to provide for the opening width of the additional outlet valve to be set as a function of the load point of the internal combustion engine. A characteristic diagram or a characteristic diagram region is assigned to the corresponding load range, there being preferably provision for the regeneration of an exhaust gas cleaning unit to be promoted in the load range with less than 50% rated power by activating an additional outlet valve.
In a further refinement of the invention, it becomes possible for the charge pressure to be influenced in conjunction with a regeneration operating mode for the internal combustion engine having an exhaust gas turbocharger. In particular there is provision, in conjunction with the regeneration operating mode, to provide for the charge pressure to be lowered. As a result of the increase in the exhaust gas temperature when an additional outlet valve is activated, an increased power output by the turbocharger can occur. This can be counteracted by means of the measure according to the invention for reducing the charge pressure. For this purpose it is advantageous if the exhaust gas turbocharger is embodied in such a way that its rotational speed can be influenced. However, the reduction of the charge pressure also permits the exhaust gas temperature to be influenced directly and is preferably provided as a increasing the temperature. It is advantageous if the corresponding settings are made possible as a function of the temperature of the exhaust gas cleaning unit.
In a further refinement of the invention, it becomes possible for the quantity of recirculated exhaust gas to be influenced in conjunction with a regeneration operating mode for the internal combustion engine having an adjustable exhaust gas recirculation device. For this purpose, an adjustable exhaust gas recirculation valve is preferably provided in the exhaust gas recirculation system. This measure makes it possible to influence effectively the exhaust gas temperature and/or the exhaust gas composition by means of the quantity of recirculated exhaust gas.
In a further refinement of the invention, the regeneration operating mode is provided when the vehicle is stationary. This measure prevents the driving mode being disrupted by the regeneration of the exhaust gas cleaning unit. The measure can additionally be provided as an emergency regeneration if an increased regeneration demand, preferably in the form of an increased degree of blocking of a filter is detected. An increased rotational speed of the internal combustion engine is preferably set when the vehicle is stationary. In this way, the conditions which are necessary for regeneration of the exhaust gas cleaning unit can also be set when the vehicle is stationary.
For the method according to the invention there is provision that, the additional outlet valve of at least one cylinder is opened at least temporarily in conjunction with a regeneration operating mode for regenerating an exhaust gas cleaning unit which is arranged in the exhaust line.
In addition to the activation of the additional valve according to the invention in order to promote the regeneration of the corresponding exhaust gas cleaning unit, the additional valve can, of course, continue to be activated or opened in order to boost the braking effect in the braking mode.
When one cylinder is provided with an additional outlet valve, it is possible to provide that when the additional outlet valve is activated said valve is operated in a fired fashion or even in an unfired fashion. In the former case, the internal combustion engine is preferably in the traction mode with a positive power output to the drive unit, and in the case mentioned second the internal combustion engine is preferably in the braking mode or under over-run conditions. In both cases it is possible to provide for the additional outlet valve of one cylinder, or if appropriate of a plurality of cylinders, to be kept at least partially in an opened state.
In one refinement of the method, at least one cylinder is operated with an at least temporarily opened additional outlet valve and with a fuel supply which is reduced compared to the normal operating mode. In this context, the reduction of the fuel supply can also include shutting it down completely. Normal operating mode is understood here to be the corresponding operating point of the internal combustion engine at which the corresponding additional outlet valve remains unactivated, i.e. continuously closed. It is basically advantageous to provide for the optional reduction in the fuel supply at all the cylinders, irrespective of whether or not they have an additional output valve.
The power output or power drain of the cylinder and thus the intensity of the heat which is output to the exhaust gas via the opened additional outlet valve can be set very effectively and adapted to the thermal demand of the exhaust gas cleaning unit by reducing the fuel supply. When there is a very large reduction in the fuel supply, combustion no longer occurs in the cylinder and the cylinder is operated in an unfired state. If the fuel supply is not shut down completely, in this case unburnt fuel is fed into the exhaust gas through the opened additional outlet valve and the exhaust gas is thus enriched with reducing agents. In this way it is possible, for example, to promote reductive regeneration of an exhaust gas cleaning unit or heat can be released in the exhaust section by post-combustion of the unburnt fuel.
In a further refinement of the method, there is provision for the additional outlet valve of at least one cylinder to be kept open in the region of the top dead center in the compression stroke, and otherwise kept closed, during a multiplicity of working cycles of the cylinder.
In this operating mode, the corresponding cylinder is operated in a braked fashion since previously compressed gases from the cylinder escape into the exhaust line without carrying out expansion work. When the cylinder is fired, these gases are very hot and the exhaust gas is correspondingly heated up to a high degree. If the fuel supply to the respective cylinder is reduced or shut off, the input of heat into the exhaust gas is correspondingly lower.
In a further refinement of the method, the additional outlet valve of at least one cylinder is kept continuously open during a multiplicity of working cycles of the cylinder. In this operating mode also, the corresponding cylinder is operated in a braked fashion even if the braking effect and the input of heat into the exhaust gas are reduced. However, the expenditure in terms of control is also lower.
In a further refinement of the method, at least one cylinder of the internal combustion engine, in particular a cylinder with an additional outlet valve, is operated with a reduced fuel supply. In this context at a cylinder with an additional outlet valve said valve can be kept temporarily opened or temporarily closed. The reduction in the fuel supply can also comprise shutting it down completely here. In this way it is possible in particular to carry out fine adjustment of the regeneration conditions. It is possible to set both the exhaust gas temperature and the exhaust gas composition, in particular the oxygen content of the exhaust gas. At the same time, the power output can be finely set, as a result of which fluctuations in the torque can be avoided.
In a further refinement of the method, at least two preferably adjacent cylinders are provided with an additional outlet valve and their additional outlet valves are activated synchronously. By grouping cylinders with respectively synchronously operated additional outlet valves it is possible to avoid, or minimize, degradation of the smooth running, and actuation is also made easier.
In a further refinement of the method, in an internal combustion engine with at least two cylinders with an additional outlet valve the number of cylinders with an at least temporarily opened additional outlet valve is set as a function of the load of the internal combustion engine. In this way it is possible to influence the exhaust gas properties very effectively. As the load or rotational speed of the internal combustion engine decreases, an increasing number of cylinders is preferably operated with an at least temporarily opened additional outlet valve. The number of corresponding cylinders may be predefined here by regions of characteristic diagrams.
In a further refinement of the method for operating an internal combustion engine having an exhaust gas turbocharger, a reduced charge pressure is set in conjunction with the regeneration operating mode. In this way it is possible in particular to influence additionally the exhaust gas temperature. The reduction in the charge pressure is preferably brought about by reducing the rotational speed by means of a blade adjustment or a waste gate adjustment of the corresponding exhaust gas turbocharger.
In a further refinement of the method for operating an internal combustion engine having an adjustable exhaust gas recirculation device, an increased quantity of recirculated exhaust gas is set in conjunction with the regeneration operating mode. This measure is expedient in particular for fine adjustment of the regeneration conditions and is preferably used in conjunction with other measures for influencing the exhaust gas temperature and/or the exhaust gas composition.
In a further refinement of the method, the regeneration operating mode is carried out when the vehicle is stationary. This can be done during an interruption of the normal driving mode or as part of a visit to a workshop. These measures permit, for example, excessively long regenerations to be carried out which cannot be carried out during the normal driving mode owing to changing operating conditions.
Advantageous embodiments of the invention are illustrated in the drawing and will be described below.